In a conventional manner, particularly for the reception of data or control signals, this type of electronic circuit 1 may comprise the electronic components shown in FIG. 1 for the automatic gain control of an input amplifier 2. This input amplifier 2 is connected directly or via a shaping stage to an antenna receiving data and/or control signals (not shown). Input amplifier 2 amplifies an input signal VIN in the automatic gain control loop with an adapted gain based on the signal or signals picked up by the antenna. The output signal VOUT which is an alternating signal dependent on the incoming signal carrier frequency, is supplied to a conventional peak detector 3. The peak detector 3 outputs a rectified signal VP, which may be continuous and which represents the amplitude of input signal VIN amplified by input amplifier 2. This rectified signal VP may be stored in a capacitor CP of peak detector 3.
Electronic circuit 1 further includes an amplifier-comparator 4, which determines an error between the rectified signal VP representative of the amplitude of signals VOUT amplified by input amplifier 2, and a reference signal VR. The rectified signal and the reference signal are generally a rectified voltage VP and a reference voltage VR supplied to the input of amplifier-comparator 4. Rectified voltage VP is supplied to the negative input, whereas reference voltage VR is supplied to the positive input of amplifier-comparator 4. According to the error determined between the two compared voltages, an adaptation signal in the form of an adaptation current or voltage VAGC is delivered by amplifier-comparator 4 to the input amplifier to adapt the gain of said input amplifier 2. An integration capacitor CINT is also arranged at the output of amplifier-comparator 4, if the amplifier-comparator output signal is in the form of a current. This amplifier-comparator 4 may be defined as a transconductance unit or an OTA operational transconductance amplifier. The gain of input amplifier 2 is adapted to a stable operating value, until the difference between the rectified voltage VP and the reference voltage VR becomes close to zero.
Although not shown in FIG. 1, the output of input amplifier 2 of the electronic circuit can be connected to a mixer unit. The mixer unit can convert the frequency of the signals picked up by the antenna and amplified by the input amplifier by means of at least one oscillating signal from a local oscillator. The intermediate signal or signals outputted by the mixer unit may thus be converted to a low frequency and even directly into base band before a data or control signal demodulation operation in a demodulator. In order to be able to demodulate the data properly, the amplitude of the signals amplified by the input amplifier must be adapted in the automatic gain control loop.
If there is a significant difference between the expected incoming signal amplitude and reference signal amplitude, fast adaptation of the input amplifier gain is required, in order for all the data demodulation operations to be performed. The setting time of the automatic gain control loop must therefore be decreased to rapidly achieve a stable operating point of the electronic circuit.
US Patent Application No. 2009/0117868 A1, which discloses an electronic circuit for the automatic gain control of a radio receiver with fast setting of gain adaptation, can be cited in this regard. The electronic circuit includes an input amplifier, whose gain can be adapted. This input amplifier receives signals picked up by an antenna and filtered and shaped by a shaping stage. The amplifier output signal is connected to a demodulator to determine the data of the signals picked up by the antenna. The demodulator output signal, which may be an output voltage, is compared to a first reference level in a first comparator and to a second reference level in a second comparator. The second reference level is defined to be greater than the first reference level. The output of each comparator is connected to a gain control terminal of the input amplifier.
The first comparator delivers a first comparison current, which is smaller than the second comparison current of the second comparator. If the demodulator output voltage is between the first threshold level and the second threshold level, a low amplifier gain setting is performed. However, if the demodulator output voltage is above the second threshold level, the two currents of the two comparators are added together to perform a fast gain setting of the input amplifier. Thus, dual slope adaptation is performed in the automatic gain control loop. However, the design of this type of electronic circuit is relatively complicated to reduce the setting time of the automatic gain control loop, which is a drawback. Moreover, fast gain adaptation cannot easily be taken into account when the demodulator output voltage is below the first threshold level, which is another drawback.
US Patent Application No 2004/0009758 A1, which discloses a fast response automatic gain control electronic circuit for narrow band systems, may be also be cited. The electronic circuit includes, in particular, an input amplifier, whose gain can be adapted in an automatic gain control loop. The input amplifier amplifies an input signal from signals picked up by an antenna to deliver an amplified signal to a mixer for low frequency conversion. The mixer outputs base band signals formed of an in-phase baseband signal I and a quadrature baseband signal Q. An AGC loop detector sets a level of the sum of the squares of the in-phase and quadrature signals to deliver an output signal to an integration capacitor. This integration capacitor is connected via a drive device to a gain control terminal of the input amplifier.
When the AGC control loop is in a closed state, parabolic adaptation occurs to adapt the input amplifier gain, which reduces the setting time of the automatic gain control loop, if the detected level is high relative to the desired incoming signal level. However, to perform this adaptation in the automatic gain control loop, many relatively complicated electronic components must be used, which is a drawback. Further, this does not facilitate the electronic testing of the electronic circuit, which is another drawback.